As a instructor, I can tell you that this is usually false...especially for a new shooter...because they don't really understand how it should feel in their hand. That is why most folks put on grips which are too large for their hands...it gives them more to hang onto. It makes them more comfortable, but not more accurate.For instance if your a NEWBIE target shooter & your comparing three different target handguns that are all of equal quality, one of the three fits YOUR hand perfectly. You will shoot that one more accurately than the other two.
TRUE or FALSE?
How comfortable a gun feels in your hand is highly overrated for new, casual or hobby shooters. It is much more important for an Olympic class shooter...but only when that bullet that strays out of the X-ring, into the 10-ring, would make a difference.
The other point I would disagree with is excessive practice without formal instruction. The oft quoted Practice Makes Perfect is just that..oft quoted. That doesn't make it true.
Practice Makes Permanent. So if you not using correct technique to begin with, you'll make those bad habits permanent...which might easily take 1000 rounds to break/overcome